Turbomachine wheels and methods of making the same



Oct. 28, 1958 D. J. BLOOMBERG TURBOMACHINE WHEELS AND METHODS OF MAKINGTHE SAME Filed Sept. 5. 1954 2 Sheets-Sheet 1 m w 5) W ml M x %////7//L\ MM 1 M 03W -& W

4 l u flifflflflflflfll% y lllffllliffllll/rllyl/ I! United StatesPatent @fiice 2,858,102 Patented Oct. 28, 1958 TURBOMACIUNE WHEELS ANDMETHODS OF MAKING THE SAME David J. Bloornberg, Newton, Mass., assignorto General Electric Company, a corporation of New York ApplicationSeptember 3, 1954, Serial No. 454,175

3 Claims. (Cl. 253-3915) The present invention relates to turbomachinewheels and methods of making the same.

It is a general object of the present invention to provide aturbomachine wheel including a disk and a plurality of circumferentiallyspaced-apart and radially outwardly extending buckets carried by theperiphery of the disk, and comprising an improved and simplifiedarrangement for rigidly securing the buckets to the disk and for rigidlysecuring together the individual elements of each bucket and forachieving etfective circulation of cooling air through the individualelements of each bucket.

Another object of the invention is to provide in a turbomachine wheel ofthe character noted, a bucket construction of improved and simplifiedarrangement, wherein the component elements thereof are formed ofmaterials especially selected to fulfill the individual operatingrequirements thereof with respect to stresses, temperatures and relatedfactors.

Another object of the invention is to provide a turbomachine wheelbucket construction including an inner post formed of high-stressmaterial especially selected to withstand the loads imposed thereon dueto centrifugal force, gas bending forces, misalignment forces, and thelike, and an outer shell formed of temperature-resistant materialespecially selected to withstand the high temperature of the working gasmedium, and embodying an improved arrangement for providing a rigidconnection between the inner post and the outer shell.

Another object of the invention is to provide a turbomachine wheelbucket construction of the character described, that comprises animproved arrangement for providing a rigid connection between the innerpost and the outer shell, and that consists essentially of first andsecond interference partsrespectively formed integrally with the outersurface of the inner post and the inner surface of the outer shell andcooperating with each other to provide an interference fit therebetween,and accommodating thepassage through ducts formed therein of cooling airbetween the inner and outer ends of the bucket.

Another object of the invention is to provide a turbomachine Wheelbucket construction of the character described, wherein the interferenceparts mentioned are disposed on both the leading side and the trailingside of the inner post so that cooling air is conducted through thebucket both immediately behind the leading wall of the outer shell andimmediately ahead of the trailing wall of the outer shell in ordereffectively to cool the outer shell and effectively to insulate theinner post from the high temperature of the outer shell.

A further object of the invention is to provide an improved method ofmaking a turbomachine Wheel including a metal disk and a plurality ofcircumferentially spaced-apart and radially outwardly extending bucketscarried by the periphery of the disk, wherein each. of the bucketsincludes a metal inner post and a metal Outer shell; whereby the methodinvolves an exceedingly simple first casting step for producing theouter shells in situ upon the respective outer surfaces of the innerposts, and an exceedingly simple second casting step for producing thedisk in situ fusing in place the inner ends of the inner posts of thebuckets.

A further object of the invention is to provide a method of making aturbomachine wheel bucket including a metal inner post and a metal outershell, and involving a first simple casting step in which the inner postis cast with integral first interference parts on the outer surfacethereof, and a second simple casting step in which the outer shell iscast in situ about the inner post with integral second interferenceparts on the inner surface thereof and cooperating with the firstinterference parts on the outer surface of the inner post to provide aninterference fit therebetween and a resulting rigid connection betweenthe inner post and the outer shell.

A still further object of the invention is to provide a method of makinga turbomachine wheel bucket of the character described, wherein firstnotches are formed in the first interference parts mentioned incident tothe casting thereof and second notches are formed in the secondinterference parts mentioned incident to the casting thereof whichnotches cooperate to provide ducts through the bucket between the outersurface of the inner post and the inner surface of the outer shell andaccommodating the passage of cooling air therethrough.

Further features of the invention pertain to the particular arrangementof the elements of the turbomachine wheel and of the steps of the methodof making the same, whereby the above-outlined and additional operatingfeatures thereof are attained. The invention, both as to itsorganization and method of operation, together with further objects andadvantages thereof, will best be understood by reference to thefollowing specification taken in connection with the accompanyingdrawings, in which: I

Figure 1 is a fragmentary side elevational view, partly broken away andpartly in section, of a turbomachine wheel embodying the presentinvention, and that may be made in accordance with the method of thepresent invention;

Fig. 2 is a substantially vertical sectional view of the turbomachinewheel, taken in the direction of the arrows along the line 2-2 in Fig.1;

Fig. 3 is an enlarged vertical sectional view of one of the bucketscarried on the periphery of the disk of the turbomachine wheel shown inFigs. 1 and 2;

Fig. 4 is an enlarged horizontal sectional view of the bucket, taken inthe direction of the arrows along the line 44 in Fig. 3;

Fig. 5 is another enlarged horizontal sectional view of the bucket,taken in the direction of the arrows along the line 5-5 in Fig. 3; and

Fig. 6 is a plan view of only the extreme outer end of the bucket shell,taken in the direction of the several arrows 6 in Fig. 3.

Referring now to Figs. 1 and 2 of the drawings, the turbomachine wheel10 there illustrated, and embodying the features of the presentinvention, may comprise the first-stage wheel in a plural stage gasturbine unit including a rotatable operating shaft 11. The wheel 10comprises an annular disk 12 provided with an inner hub 13 that isrigidly secured to the operating shaft 11 for rotation therewith; andthe periphery of the disk 12 carries a plurality of circumferentiallyspaced-apart and radially outwardly extending composite buckets 14,described more fully hereinafter. Also the wheel 10 comprises a pair ofannular members 15 disposed on opposite sides of the disk 12 and carriedby the opposite ends of the hub 13 and spaced laterally from therespective faces of the disk 12 to provide a pair of annular chambers 16therebetween extending radially from the hub 13 to the flange portions33 and 34 of the buckets 14. A number of circumferentially spaced-apartopenings 17 are formed in each of the members 15 adjacent to the hub 13in order to accommodate the passage of cooling air from the exteriorinto the corresponding one of the chambers 16; and in order further toassist in the circulation of cooling air into the openings 17, each ofthe members 15 carries an outwardly projecting annular ring 18 disposedradially outwardly with respect to the openings 17 and surrounding theoperating shaft 11.

The composite buckets 14 are substantially identical; and each bucket 14essentially comprises a radially extending inner post 19 and asurrounding radially extendingv outer shell 20, the inner end of theinner post 19 being fused into and forming a part of the adjacentportion of the periphery of the disk 12, and the outer end of the innerpost 19 being rigidly secured to the intermediate portion of the outershell 20. As best shown in Figs. 3 to 6, inclusive, the outer surface ofthe outer shell 20 is provided with a typical configuration defining theusual gasfoil, the leading and trailing walls of the outer shell 20being respectively indicated at 21 and 22; whereby the wheel is rotatedin the counterclockwise direction, as viewed in Fig. 1, when the workinggas medium passes through the buckets 14. The junction between the walls21 and 22 at the front of the outer shell 20 comprises a roundedsection, as indicated at 23; while the junction between the walls 21 and22 at the rear of the outer shell 20 comprises an elongated tail, asindicated at 24. Of course, the outer shell 20 is hollow, having an openouter end, and the walls 21 and 22 have a minimum thickness consistentwith the required strength thereof; and in order to conserve material, acavity 25 is formed in the outer end of the inner post 19.

As best shown in Figs. 3 and 5, the outer shell 20 is supportedintermediate the ends thereof upon the outer end of the inner post 19 bya rigid connection therebetween, whereby the inner end of the outershell 20 projects radially inwardly toward the periphery of the disk 12and in surrounding relation with respect to the adjacent portion of theinner post 19, providing a continuous space 26 therebetween, while theouter end of the outer shell 20 projects radially outwardly beyond theouter end of the inner post 19. The rigid connection mentioned betweenthe inner post 19 and the outer shell 20 is formed by an interferencefit consisting of a first series of radially spaced-apart teeth 27-formed integrally with the outer end of the inner post 19 and projectingcircumferentially outwardly therefrom, and a second series of radiallyspaced-apart teeth 28 formed integrally with the intermediate portion ofthe outer shell 20 and projecting circumferentially inwardly therefrom;the first series of teeth 27 being provided on the outer surface of theinner post 19, and the second series of teeth 28 being provided on theinner surface of the outer shell 20, and the two series of teeth 27 and28 being disposed in interfitting relation. The interfitting teeth 27and 28 are dis posed both immediately behind the leading wall 21 of theouter shell 20 and immediately ahead of the trailing wall 22 of theouter shell 20; and first and second series of spaced-apart ducts 29 and30 are formed by cooperating notches in the first and second sets ofteeth 27' and 28, the first set of ducts 29 being disposed immediatelybehind the leading wall 21 of the outer shell 20 and communicatingbetween the leading portion of the space 26 and the space 31 defined inthe hollow outer end of the outer shell 20, and the second set of ducts30 being disposed immediately ahead of the trailing wall 22 of the outershell 20 and communicating between the trailing portion of the space 26and the space 31.

The extreme lower end of the outer shell 20 terminates in an outwardlydirected flange 32 including a portion 33 extending forwardly and aportion 34 extending rearwardly, each of the flange portions 33 and 34being arranged in spaced relation radially outwardly of the root of theinner post 19, and consequently in this relationship with respect to theperiphery of the disk 12. As best shown in Fig. l, the leading flangeportion 33 carried by the outer shell 20 of each bucket 14 cooperateswith the trailing flange portion 34 carried by the outer shell 20 of theadjacent bucket 14 to provide a substantially continuouscircumferentially extending bridge therebetween defining a correspondingarcuate space 35 therebelow adjacent to the periphery 42 of the disk 12and commonly communicating between the leading and trailing portions ofthe two spaces 26 provided in the two adjacent buckets 14. Also leadingand trailing grooves 37 and 38 are respectively formed in the leadingand trailing portions of the root of each inner post 19, whereby theadjacent grooves 37 and 38 provided in the roots of adjacent inner posts19 define a laterally extending cooling air outlet passage 39communicating between the annular chambers 16 adjacent to the peripheryof the disk 12 and also communicating with the space 35. Finally, aseries of forwardly directed ribs 40 and a series of rearwardly directedribs 41 are carried below the respective flange portions 33 and 34provided on the inner end of the outer shell 20 and arranged inengagement with the root portion of the associated inner post 19, andconsequently in this relationship with respect to the periphery 42 ofthe disk 12.

In view of the foregoing description of the construction and arrangementof the wheel 10, it will be understood that when the operating shaft 11is rotated at high speed the cooling air that is drawn through the inletpassages 17 into the chambers 16 proceeds radially therethrough andthence into the opposite ends of the circumferentially spaced-apart andlaterally extending outlet passages 39 disposed adjacent to theperiphery of the disk 12. The cooling air in each outlet passage 39proceeds into the adjacent space 35 and thence into the leading andtrailing portions of the two spaces 26 provided in the adjacent leadingand trailing buckets 14. From the leading portion of the space 26 ineach bucket 14, the cooling air proceeds through the set of ducts 29into the space 31; and from the trailing portion of the space 26 in eachbucket 14, the cooling air proceeds through the set of ducts 30 into thespace 31; and ultimately the cooling air is discharged from the space 31radially outwardly through the outer open end of the outer shell 20 ofeach bucket 14. Thus, it will be understood that the two streams ofcooling air proceeding through each bucket 14, not only effectivelycools the respective leading and trailing walls 21 and 22 of the outershell 20 thereof, but it also serves efiectively to insulate the innerpost 19 from the high temperature of the outer shell 20.

In the construction of the wheel 10, the disk 12 is formed of a suitablecast metal having a relatively high strength with respect to tensionstresses in order to withstand the centrifugal load thereon resultingfrom highspeed rotation thereof; each of the inner posts 19 is formed ofa suitable cast metal having a very high strength with respect totension and torsion stresses in order to withstand the centrifugalforce, the gas bending forces and any misalignment forces to which it issubjected; while each of the outer shells 20 is formed of a suitablecast metal that is exceedingly resistant to very high temperatures (atleast 1500 F.), and that has considerable strength at such hightemperatures, with respect to tension, compression and torsion stressesin order to withstand the corresponding effects thereon produced both bycentrifugal force and by the high-temperature gas medium in contacttherewith. In this connection, it will be appreciated that when thewheel 10 is rotated at high speed, the inner end of each outer shell 20is also subjected to compression forces; the outer end of each outershell 20 is also subjected to tension forces; each inner post 19 issubjected fundamentally to tension and torsion forces; and theinterfitting teeth 27 and 28 respectively carried by each inner post19and by each outer shell 20 are subjected fundamentally to shearingforces. As a constructional example, when the wheel comprise sthefirst-stage wheel of a 600 H. P. gas turbine unit, the diameter thereofbetween the outer extremities of oppositely directed buckets 14 may beapproximately 18", each of the buckes 14 may have a radial length of theouter shell 20 thereof of approximately 1%, the leading and trailingwalls 21 and 22of each outer shell 20 may have a thickness of about hiand the other dimensions are related to those set forth in accordancewith: standard design considerations. Moreover, the disk 12 and themembers may be cast of a suitable lowcarbon steel, such, for example, asthat sold by Allegheny Ludlum under the designation A-286"; each of theinner posts 19 may be cast of a suitable chromesteel, such, for example,as the commercially available 12% chrome-steel alloy; while each of theouter shells may be cast of a suitable special alloy, such, for example,as that sold as X-40. Really, only the alloy of the outer shells 20comprises a strategic material; and the composition of the alloy X 40 isessentially as follows:

In making the turbo machine wheel 10, the plurality of composite buckets14 are first produced; and in fabricating each of the buckets 14, boththe inner post 19 and the associated outer shell 20 is formed employingrespective precision investment casting steps (the lost wax technique).More particularly, a wax pattern of the inner post 19 is first investedwith a suitable investment material (ceramic material, or the like); andthereafter, the invested wax pattern is supported in a suitable moldmaterial (sand, or the like). Then the composite mold is preheated sothat the wax pattern of the inner post 19 is melted and removed from theinvestment material, leaving a corresponding void in the supporting moldmaterial; and thereafter, the mold material is completely cured.Finally, the high-stress metal is cast into the mold filling the voiddefined by the investment material so that, upon cooling, the inner post19 is in a finished condition after rem-oval thereof from the mold andthe breaking-away of the investment material. When the inner post 19 is.thus cast, the series of teeth 27 are formed integrally with the bodythereof; and also the notches for the ultimate production of the ducts29 and 30 are formed therein incident to this casting step.

Then the cast inner post 19 is prepared for the casting thereonto of theassociated outer shell 20. More particularly, suitable cores (formed ofceramic material, or the like) are arranged upon the outer end of theinner post 19 in the notches mentioned for the ultimate production ofthe ducts 29 and 30 in the finished bucket 14. Then a wax pattern of theouter shell 20 is cast in place upon the outer end of the inner post 19;and then both the inner post 19 and the wax pattern of the outer shell20 are invested with a suitable investment material; and thereafter, thecomposite invested pattern is supported in a suitable mold material.Then the composite mold material is preheated so that the wax pattern ofthe outer shell 20 is melted and removed from the investment material,leaving a corresponding void in the supporting mold material; andthereafter, the mold material is completely cured.

Finally, the heat-resistant metal is cast into the mold filling the voiddefined by the investment material so that, upon cooling, the outershell 20 is in a finished condition after removal thereof, with theinner post 19, from the mold and the breaking-away of the investmentmaterial. When the outer shell 20 is thus cast, the series of teeth 28are formed integrally with the body thereof; and also the notches forthe ultimate production of: the ducts 29 and 30 are formed thereinincident to this casting step. Of course, the cores supported by theinner post 19 in the .casting of the outer shell 20 define the ducts 29and 30 in the composite bucket 14 after the breaking and removal ofthese cores. Moreover, in this casting of the outer shell 20, the outersurface [thereof is in a smooth and finished condition directly definingthe gasfoil, and without further finishing operation.

In view of the foregoing, it will be understood that the requiredplurality of the composite buckets 14 are fabricated; and then they arearranged in a mold in proper position in ci-rcumferentially spaced-apartrelation extending radially outwardly with the inner ends of the innerposts 19 extending radially inwardly; and then the metal of the disk 12is cast into the mold so that the inner ends of the inner posts 19 areencompassed thereby, whereby the inner ends of the inner posts 19 arefused into the metal of the disk 12 forming the periphery thereof andproviding a corresponding plurality of rigid connections between thedisk 12 and the plurality of buckets 14. After cooling of the disk 12,the partially completed wheel 10 is removed from the mold.

The annular members 15 may be cast or fabricated in any conventionalmanner; and thereafter, they are brought into place and assembled uponthe hub 13 of the disk 12. Subsequently, the annular members 15 aresecured to the hub 13 in any suitable manner, such as: welding,induction melting, etc.; whereby the wheel 10 is ready for certain finalfinishing operations, including balancing, etc.

In view of the foregoing, it is apparent that there has been provided aturbomachine wheel of improved and simplified construction andarrangement, as well as an improved method of making the same. Theimproved wheel also includes a plurality of composite buckets ofimproved and simplified construction and arrangement; and similarly, theoverall method includes improved and simplified method steps of makingthe composite buckets.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A turbomachine wheel comprising a disk and a plurality ofcircumferentially spaced-apart .and radially outwardly extending bucketsdisposed about the periphery of said disk; each of said bucketsincluding a post rigidly secured to the periphery of said disk, a shellsurrounding said post and provided with an outer surface defining agasfoil, means including a first series of teeth formed integrally withsaid post and a second series of teeth formed integrally with said shelland cooperating with each other to define an interference fittherebetween for rigidly securing said shell to said post, said firstseries of teeth being provided on the outer surface of said postadjacent to the outer end thereof and said second series of teeth beingprovided on the inner surface of said shell intermediate the endsthereof, whereby the inner end of said shell projects radially inwardlytoward the periphery of said disk and the outer end of said shellprojects radially outwardly beyond the outer end of said post, meansdefining a first duct between said post and the leading wall of saidshell, means defining a second duct between said post and the trailingwall of said shell, means including a first flange carried by the innerend of said shell and extending outwardly therefrom in the leadingdirfiction and spaced radially outwardly fromthe periphcry of said .diskfor directing cooling air into saidfirst duct," and means including asecondflange carried by the inner end of said shell and extendingoutwardly there from in the trailing direction and spaced radiallyoutwardly from the peripheryiof said disk for directing eool ing airinto said second duct.

2. The turbornachine Wheel set forth in claim 1, wherein the firstflange carried by each shell cooperates with the second flange carriedby the adjacents'nell to provide a substantially continuouscircumferentially extending bridge therebetween.

3. Thetturbomachine heel set forth inclaim 1, Wherein the first andsecond flanges carried by each shell re spectively carry first andsecond sets of-radially inwardiy directed supporting ribs engaging theperiphery of said disk.

References Cited .in the file of this 1 patent UNITED STATES PATENTSBuchi Nov. 29, .Klenk Mar. 15, Dimberg Mar. 15, ,Dirnberg -Mar. l5,Fransson Mar.t2 1, Franz .S ept. 2 5, .Johnstone May'27, Schmitt Aug.11, Williams Nov. 3, Grantham July 27, Bruckman Jan. 29,

FOREIGN PATENTS Great Britain Jan. 20,

